Re: [PATCH v2 6/6] mm/mm_init: Fix pageblock migratetype for ZONE_DEVICE compound pages

Mike Rapoport
2026-04-15T17:03:20Z

Hi Muchun,

On Wed, Apr 15, 2026 at 07:14:12PM +0800, Muchun Song wrote:
> The memmap_init_zone_device() function only initializes the migratetype
> of the first pageblock of a compound page. If the compound page size
> exceeds pageblock_nr_pages (e.g., 1GB hugepages with 2MB pageblocks),
> subsequent pageblocks in the compound page remain uninitialized.
>
> Move the migratetype initialization out of __init_zone_device_page()
> and into a separate pageblock_migratetype_init_range() function. This
> iterates over the entire PFN range of the memory, ensuring that all
> pageblocks are correctly initialized.
>
> Fixes: c4386bd8ee3a ("mm/memremap: add ZONE_DEVICE support for compound pages")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/mm_init.c | 42 +++++++++++++++++++++++++++---------------
> 1 file changed, 27 insertions(+), 15 deletions(-)
>
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index f9f8e1af921c..30528c4206c1 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -674,6 +674,19 @@ static inline void fixup_hashdist(void)
> static inline void fixup_hashdist(void) {}
> #endif /* CONFIG_NUMA */
>
> +static __meminit void pageblock_migratetype_init_range(unsigned long pfn,
> + unsigned long nr_pages,
> + int migratetype)
> +{
> + unsigned long end = pfn + nr_pages;
> +
> + for (pfn = pageblock_align(pfn); pfn < end; pfn += pageblock_nr_pages) {
> + init_pageblock_migratetype(pfn_to_page(pfn), migratetype, false);
> + if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
> + cond_resched();
> + }
> +}
> +
> /*
> * Initialize a reserved page unconditionally, finding its zone first.
> */
> @@ -1011,21 +1024,6 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
> page_folio(page)->pgmap = pgmap;
> page->zone_device_data = NULL;
>
> - /*
> - * Mark the block movable so that blocks are reserved for
> - * movable at startup. This will force kernel allocations
> - * to reserve their blocks rather than leaking throughout
> - * the address space during boot when many long-lived
> - * kernel allocations are made.
> - *
> - * Please note that MEMINIT_HOTPLUG path doesn't clear memmap
> - * because this is done early in section_activate()
> - */
> - if (pageblock_aligned(pfn)) {
> - init_pageblock_migratetype(page, MIGRATE_MOVABLE, false);
> - cond_resched();
> - }
> -
> /*
> * ZONE_DEVICE pages other than MEMORY_TYPE_GENERIC are released
> * directly to the driver page allocator which will set the page count
> @@ -1122,6 +1120,8 @@ void __ref memmap_init_zone_device(struct zone *zone,
>
> __init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
>
> + cond_resched();
> +

I don't think we want cond_resched() for every page here too, even it's a
compound page :)

Otherwise

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> if (pfns_per_compound == 1)
> continue;
>
> @@ -1129,6 +1129,18 @@ void __ref memmap_init_zone_device(struct zone *zone,
> compound_nr_pages(altmap, pgmap));
> }
>
> + /*
> + * Mark the block movable so that blocks are reserved for
> + * movable at startup. This will force kernel allocations
> + * to reserve their blocks rather than leaking throughout
> + * the address space during boot when many long-lived
> + * kernel allocations are made.
> + *
> + * Please note that MEMINIT_HOTPLUG path doesn't clear memmap
> + * because this is done early in section_activate()
> + */
> + pageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE);
> +
> pr_debug("%s initialised %lu pages in %ums\n", __func__,
> nr_pages, jiffies_to_msecs(jiffies - start));
> }
> --
> 2.20.1
>

--
Sincerely yours,
Mike.